Tuesday, November 19, 2013

It swims in the ocean, dances on water and glides through air, what is it? Not much of a riddle since the solution is in the title, but how bizarre that a single family of fish evolved to achieve three feats of which most animals can perform only one.

Patricia Yang, a graduate student of mechanical engineering at the Georgia Institute of Technology, raises flying fish in a tank in Taiwan. She is one of the few scientists around the world to study flying fish in a laboratory setting instead of their natural environment. In the lab, she could get a close look at the initial steps any fish must make before taking flight. One being breaking the surface-tension barrier between water and air.

Credit: Theron Trowbridge

While the fish were still in their juvenile state, measuring no longer than two centimeters, Yang and a group of scientists from Georgia Tech and the National Sun Yat-sen University in Taiwan trained them to launch into the air on command. Using high-speed videography, the team examined the speed and angle with which the flying fishlings broke the water’s surface.
To large fish and other marine animals, like dolphins, penguins and seals, the ocean’s surface is easily penetrable. But to a small juvenile flying fish, the surface is a formidable barrier that must be broken with great force.

The scientists extrapolated the data from their videography footage to calculate the acceleration rate of the fish upon breaching the surface. Over the course of .05 seconds, a tenth of the time it takes to blink your eye, the fish achieved accelerations of up to five times earth’s gravity.

That level of g-force is rough on the human body because it forces blood toward the feet and in the process deprives the brain of oxygen, which can lead to loss of consciousness. Some high-G roller coasters can reach accelerations between four and five times earth’s gravity. The affect that 5 G has on the juvenile flying fish is yet to be determined, Yang said.

Once the fish shot from the water, they reached gliding speeds up to 1.3 meters per second, the team measured. At this rate, the fish were traveling ten times faster gliding through air than swimming in water. Gliding capability is a handy escape-mechanism for flying fish when mealtime comes around and their winged-fins are on the menu.

Flying fish must reach a certain size, however, before they can generate enough force to breach the surface and gleefully glide away from predators. The team found that when they signaled the fish to swim to the surface, juveniles less than one centimeter long simply bounced against the surface instead of penetrating it.

Therefore, size and speed are important components for flying fish, as well as any other animal that dabbles both in air and underwater. The team aims to observe larger animals in the future to determine what kinds of g-force animals like penguins and seals experience when shooting from water to air.

The team published their results in an abstract for the 66th Annual Meeting of the APS Division of Fluid Dynamics. They will present their work in more detail at the meeting, which will take place in Pittsburgh from November 24-26.

Yang hopes to continue studying the fish as they mature into adult flying fish. For that, she said, they will need a bigger tank.